Why Two Charts of the Same Pair Never Match Tick for Tick

[Shadow Trader]

A forex price is not a single official quote. No central exchange exists, so each broker builds its own feed by aggregating quotes from liquidity providers, then applying its own filtering and markup.

As a result, tick sequences differ between brokers. One feed may show a brief spike that another filters out as an outlier, and highs and lows of one-minute candles can disagree by a fraction of a pip. For a scalper working with tight targets, that difference can decide whether a limit order would have filled.

Tick history used for backtesting adds another layer. Data from third-party sources may be modeled from lower-timeframe bars or may reflect a different liquidity pool and spread than the broker where trades are actually placed. Variable spreads are often approximated by a fixed value in tests, which understates costs around news.

Comparing a strategy's signals on the live feed to the same signals computed on historical data is revealing. Gaps between the two hint at quality issues. Using the broker's own tick history, where available, reduces the mismatch, though no dataset perfectly reproduces live conditions.